The present invention relates generally to circuits for providing clocking signals and more specifically to techniques for improving the power consumption of a real time clock.
Crystal oscillators are often used to provide a clock signal to a data processing application. For many devices, the crystal oscillator is powered all of the time. Typically, when crystal oscillators are used in a real time clock application, lithium batteries are often used to provide power. Lithium batteries can have a life span of many years when the oscillator dissipates only a minimal amount of power.
However, reducing power consumption for contemporary high speed Complementary Metal Oxide Semiconductor (CMOS) devices, such as CMOS devices at 0.13 micro-meters or less, can be difficult. These high performance devices typically use lower circuit threshold transistors, which can have considerable leakage currents. Another problem with these devices is that their power supply voltages can vary. For example, typical 0.13 micro-meter CMOS device uses a 1.5 Volt power supply, and a 90 nano-meter CMOS device usually uses a 1.2 volt power supply, while the typical lithium battery supplies 3V. Thus, a real time clock that dissipates a minimal amount of power is desirable. Furthermore, it is desirable that the real time clock can be implemented using high performance CMOS devices.